Technology update

Jul 17, 2008

CNTs reinforce alumina composites

Scientists in Japan have found that "pitted" multiwalled carbon nanotubes (MWCNTs) are ideal for reinforcing alumina (Al2O3) composites. According to the team from Tohoku University, applications could include prosthetic joints and MEMS as the MWCNTs strengthen the material and lubricate the surface.

Researchers have tried to incorporate carbon nanotubes into a ceramic matrix before, hoping to produce a tough, highly stiff and thermostable composite. Unfortunately, the result is often disappointing, with little or sometimes no improvement in material properties.

One of the problems is phase segregation and in the current work the team uses a well known acid-etch process to make the MWCNTs much easier to disperse in the matrix.

What is interesting is that the pitted surface of the acid etched carbon nanotubes appears to play a key role in locking the ceramic composite together.

The team found that the bending strength and fracture toughness of their acid-treated MWCNT/alumina composites were always higher than versions made using pristine MWCNTs. Even though the amount of nanomaterial was identical in each case, the smooth nanotubes provided less reinforcement.

Adding as little as 0.9% by volume of acid-treated MWCNTs resulted in a 27% increase in bending strength and a 25% increase in fracture toughness compared with test samples of pure Al2O3.

"We are still investigating the idea, but we believe that the improvement in the mechanical properties of the composites may be attributed to an enhanced frictional resistance between the acid-treated MWCNTs and the matrix material," Go Yamamoto told nanotechweb.org. "Currently, we are looking into the force required to separate MWCNTs from a solid alumina matrix."